Fixtures such as shower heads are normally supplied with hot water by way of piping located between the shower head and a hot water source such as a water heater. The hot water that remains in the piping when the flow to the shower head is stopped normally cools over time. The piping itself also cools once the flow of hot water therethrough has stopped.
The presence of the relatively cold water in the hot water supply pipe causes a delay between the time at which flow to the shower head is re-started, and the time at which warm water begins to flow from the shower head. The relatively cold water needs to be purged from the hot water supply pipe, and the temperature of the pipe may need to be increased, before warm water can reach the shower head.
The time required to purge the cold water from the hot water supply pipe and warm the pipe is dependent upon the overall length of the pipe, and the flow rate through the shower head. In particular, the required time increases with the overall length of the hot water supply pipe. The required time also increases as the flow rate through the shower head decreases.
A current trend in new-home construction is to deliver hot water from the water heater to multiple fixtures in multiple rooms using a single run of piping with individual branches emanating therefrom. The use of a single piping run to service multiple rooms can reduce the overall amount of copper piping needed to construct the house. This arrangement, however, can increase the volume of water between the water heater and some of the fixtures, and can thereby increase the volume of cold water that needs to be purged from the piping, and the amount of piping that needs to be warmed, before warm water can be delivered to the fixtures. Another trend is the construction of larger houses, which in general can increase the distance that water from the water heater needs to travel before reaching any specific fixture or outlet.
A further trend in new-home construction is the use of low-flow shower heads and other fixtures that limit the flow of water therethrough to relatively low levels, e.g., 2.2 gpm (gallons per minute) at 80 pounds per square inch (psi) pressure, to conserve water. The low flow rate through such fixtures tends to increase the time needed to purge cold water from the hot water supply pipe and warm the pipe after the flow to the fixture has commenced.
The use of long piping runs, low flow rate fixtures, and other factors can thus increase the delay between the time at which a shower or other water source is turned on, and the point at which the water flowing from the source reaches a comfortable level. In some cases, the delay can be excessive, and can represent a substantial inconvenience to the user.